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This study was done to describe the synoptic and mesoscale events associated with the development of fog and stratus along the Central California Coast during the 30 April to 5 May 1990 period. These events were compared and contrasted to the synoptic and mesoscale evolution found for stratus surge and Catalina Eddy events. Based on the analysis, the formation of the stratus and fog was found to be initiated by the movement of an upper- level cut-off low and a shortwave ridge. Their movements provided increased subsidence and upper-level negative vorticity advection (NVA lover Southern California, which, in turn, produced higher pressure over the Vandenburg region. This coupled with relatively lower pressure over Oakland, set up flow conditions that lead to the formation of the stratus and fog. The Vandenburg/Oakland pressure gradient produced southerly flow, which carried warm moist air over relatively cooler water. The moist air condensed and stratus and fog developed., http://archive.org/details/synopticmesoscal00cork, Lieutenant Commander, United States Navy, Approved for public release; distribution is unlimited.

The mesoscale vertical structure of an explosively deepening oceanic cyclone on 19-20 January 1989 during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) was studied. Hand analyses of height, temperature, and dewpoint, and cross-sections of 6 and 6, were prepared using aircraft and sounding data through the warm-frontal region in order to document the vertical structure. The results showed that the initial disturbance formed under a region of strong upper-level confluence between a southern jet streak and an approaching upper-level short-wave from the northwest. Upper-level frontogenesis associated with the confluent flow was strong enough to produce tropopause folding and stratospheric extrusion as low as 700 mb about 750 km upstream from the surface low prior to rapid deepening. The mesoscale analyses during the initial occlusion phase showed the upper-level temperature and moisture patterns spiraling around the low center with strong warm air advection occuring under a pocket of cold air aloft, producing significant convective instabilty. The cross-sections of 6f throughout the rapid deepening period showed unstable conditions, which suggests that moist potential instability in the warm frontal region was a factor in the rapid development of this storm., http://archive.org/details/mesoscalevertica1094528354, Captain, United States Air Force, Approved for public release; distribution is unlimited.

The mesoscale surface structure of an explosively deepening storm that developed during Intensive Observation Period (IOP) 5 (18-20 January 1989) of the Experiment on Rapidly Deepening Cyclones over the Atlantic (ERICA) was examined to determine the influence of surface forcing on explosive cyclogenesis. Aircraft, buoy and ship observations were converted to a 20 km gridded data set in order to generate objective analyses of the surface pressure and temperature fields comparable to the best hand analyses. The Brown-Liu boundary layer model was then used to calculate surface sensible heat fluxes from the gridded data sets. These analyses showed that the most significant feature that distinguished the IOP-5 storm from a typical nonexplosive storm was the region of sustained positive heat fluxes that occurred east of the low center. This feature, combined with substantial warm advection and conditions of moist symmetric neutrality in the baroclinic zone of the warm front, supports destabilization of the boundary layer and enhanced low-level baroclinicity. Thus, the positive heat fluxes fuel the convective transport of heat and moisture to the upper atmosphere and enhance the sensible and condensation heating that contribute to explosive cyclogenesis, http://archive.org/details/mesoscalesurface1094526626, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

NOAA-7 AVHRR data from April 1982 was used to perform global-scale analysis of aerosol particle characteristics. Mahony's (1991) water vapor correction was incorporated into the AVHRR multichannel satellite data processing technique used by Frost (1988). Channel 4/Channel 5 brightness temperature difference was used as an estimate of water vapor content in an air column. Greatest measured water vapor content was at the equator, decreasing toward the poles. Applying the correction reduced the aerosol particle size index, resulting in an increase in aerosol optical depths. In addition, the high particle size index over the low latitudes in the southern hemisphere noted by Frost, was reduced significantly after applying the correction. A comparison was made between Frost's values for the variable two-term Henyey-Greenstein phase function and those derived with the water vapor correction. The basic shape of the curve is similar to that determined bv Frost., http://archive.org/details/effectsofwaterva1094528152, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

Upper fronts are associated with strong horizontal gradients of both temperature and wind speed on a scale that is not well resolved by rawinsonde observations. Even so, mesoscale data assimilation systems are capable of ingesting observations from a variety of sources and depicting such features. This study examines upper fronts that occurred over the continental U.S. during March-April 1996 with the objective of verifying the performance of the NORAPS (Navy Operational Regional Atmospheric Prediction System) data assimilation system using ACARS (ARINC Communications, Addressing, and Reporting System) aircraft observations. ACARS observations are taken every 5 to 8 minutes during level flight, which yields a horizontal resolution along the flight track of less than 100 km and so can resolve the approximately 200 km width scale for upper fronts. The ACARS temperature observations are not currently used in the data assimilation system and so present an independent set of observations. Thirty distinct upper fronts (duration greater than 12 h and temperature gradient greater than 2 deg C/100 km) were identified and tracked from the NORAPS analyses during the period of the study. In general, the analyzed temperature gradient was weaker than that observed in the ACARS data. The latter depicted a temperature gradient of 8 deg C/100 km for two cases, whereas the analyzed gradient did not exceed 6 deg C/100 km. Most upper fronts (47%) attained maximum intensity when located in the base of the upper level trough, although 33% (13%) did so just downstream (upstream) of the trough line. Most of the useable aircraft tracks were near 200-300 mb, therefore the portion of the upper front above the tropopause was examined in greater detail than the portion below the tropopause, although the latter would be expected to contain stronger temperatui->h(0g(2gd4i((*", http://archive.org/details/acomparisonofupp1094525757, Lieutenant, United States Naval Reserve, Approved for public release; distribution is unlimited.

Variations in marine stratocumulus microphysics during FIRE IFO 1992 are observed and analyzed through the use of NOAA 10/11/12 AVHRR satellite data. Maritime and continental aerosols in clear-air and cloudy regions are characterized by particle size index, optical depth, and low cloud analysis at visible and 3.7 pm wavelengths. Use of satellitedetected radiances to resolve aerosol type and distribution prove useful in determining implications of cloud reflectance changes due to modification by aerosol particles. Air masses were clearly defined and showed distinctive signatures in aerosol characteristics and cloud reflectances at 3.7 pm wavelengths. Air mass characteristic sources consisted of industrial aerosols out of Europe and desert dust from the Sahara Desert., http://archive.org/details/amaritimendconti1094523949, Lieutenant, United States Naval Reserve, Approved for public release; distribution is unlimited.

Difficulty analyzing mesoscale features in California and Nevada for a 1991 case study prompted a review of techniques for sea level pressure (SLP) reduction and an evaluation of the performance of the various techniques for the U.S. west coast states at 0000 UTC 30 November 1991. The objective of any SLP reduction procedure is to provide a pressure field that portrays meteorological features rather than terrain features, a difficult goal to meet in this region given the steep terrain gradients on the western slopes of the Sierra Nevada range. The review and evaluation are performed both for techniques applicable at individual stations and for techniques applicable at grid points in a model analysis or forecast. When using station data, one would like to perform a manual or objective analysis of SLP with the greatest number of stations possible by adding stations that report only altimeter setting to the stations that report both SLP and altimeter setting. The results of the comparison show that the incorporation of altimeter-setting stations into an analysis of SLP was found to be practical only at elevations less than 300 m. Above this, the standard reduction includes empirical corrections that cannot be easily duplicated, and the other reduction techniques yielded values that varied over a large enough range that the uncertainty associated with the choice of technique becomes too great to permit the analysis of weak mesoscale features. At such low elevations, the various techniques examined gave similar results; therefore, the simple reduction is recommended. In elevated plateau regions, a pressure analysis on a geopotential surface at approximately the mean terrain height is recommended to minimize reduction errors. No satisfactory solution was found for regions with steep terrain gradients. Computing SLP from model objective analyses or forecasts that are in the model’s native vertical coordinate, typically the terrain-following sigma coordinate, poses a differ

High surface winds over California and the bordering Pacific Ocean resulted in the death of one man and the loss of power to approximately 50,000 residences across the state. These damaging winds are hypothesized to result from an upper level front and associated tropopause folding that rapidly intensify as they move south across the region, causing high momentum air to be transported to the lower troposphere. Once the high momentum air reaches the top of the planetary boundary layer, the combined effects of destabilization of the planetary boundary layer by cold air advection aloft and shear induced turbulence at the top of the layer provide the initial mechanism by which the high momentum air is entrained into the layer and mixed to the surface. After sunrise, convectively driven turbulence provides an additional source of mixing in the planetary boundary layer. The high surface winds have a strong cross isobaric component in the direction of the upper level winds, and the upper level frontal movement to the south over central California is synchronous with the increase of surface winds over the same region. The winds decrease as the upper level front moves into the base of the upper level trough and the high momentum source in the lower troposphere disappears.

Upper fronts are associated with strong horizontal gradients of both temperature and wind speed on a scale that is not well resolved by rawinsonde observations. Even so, mesoscale data assimilation systems are capable of ingesting observations from a variety of sources and depicting such features. This study examines upper fronts that occurred over the continental U.S. during March-April 1996 with the objective of verifying the performance of the NORAPS (Navy Operational Regional Atmospheric Prediction System) data assimilation system using ACARS (ARINC Communications, Addressing, and Reporting System) aircraft observations. ACARS observations are taken every 5 to 8 minutes during level flight, which yields a horizontal resolution along the flight track of less than 100 km and so can resolve the approximately 200 km width scale for upper fronts. The ACARS temperature observations are not currently used in the data assimilation system and so present an independent set of observations. Thirty distinct upper fronts (duration greater than 12 h and temperature gradient greater than 2 deg C/100 km) were identified and tracked from the NORAPS analyses during the period of the study. In general, the analyzed temperature gradient was weaker than that observed in the ACARS data. The latter depicted a temperature gradient of 8 deg C/100 km for two cases, whereas the analyzed gradient did not exceed 6 deg C/100 km. Most upper fronts (47%) attained maximum intensity when located in the base of the upper level trough, although 33% (13%) did so just downstream (upstream) of the trough line. Most of the useable aircraft tracks were near 200-300 mb, therefore the portion of the upper front above the tropopause was examined in greater detail than the portion below the tropopause, although the latter would be expected to contain stronger temperatui->h(0g(2gd4i((*"

Quantitative predictions of surface extratropical cyclone development are correlated to the degree of upper-level forcing from 500 mb vorticity advection and 300 mb divergence. Although it is difficult to obtain an accurate analysis of upper-level divergence, modern models and data assimilation procedures do produce consistent divergence fields. The divergence field partitioned into the longitudinal (alongstream) and transverse (cross-stream) components approximately estimates the effect of curvature and jet streaks on cyclone intensification. Verification of the Eta model indicated not significant difference in the mean central pressure to a confidence level of 95%, and verification of the 300 mb divergence was very similar to the 500 mb vorticity advection. The presence of subgeostrophic flow in the trough and supergeostrophic flow in the ridge was noted with the longitudinal divergence. Large variability in longitudinal divergence reflected some sensitivity to small-scale perturbations in the height field. Transverse divergence showed greater consistency and projected a similar wind pattern to the classic jet streak model, however, modifications were seen as ageostrophic winds may also be directed toward regions of height falls. The composition of the total divergence from the longitudinal and transverse divergence is about 50:50. However, with very large total divergence values, the dominant contributor is the transverse divergence.

On 29 November 1991 a series of collisions involving 164 vehicles occurred on Interstate 5 in the San Joaquin Valley in California in a dust storm that reduced visibility to near zero. The accompanying high surface winds are hypothesized to result from intense upper-trophospheric downward motion that led to the formation of a strong upper front and tropopause fold and that transported high momentum air downward to midlevels where boundary layer processed could then mix it to the surface. The objectives of the research presented in this paper are to document the event, to provide support for the hypothesis that both upper-level and boundary layer processes were important, and to determine the structure of the mesoscale circulations in this case for future use in evaluating the navy's mesoscale data assimilation system...

Assessment of the performance of the National Meteorological Center's (NMC) new Eta numerical weather prediction model requires objective evaluation through direct comparison of model forecast output to its own analysis and to the analysis of other numerical models. The ultimate goal of the Eta Model is to provide accurate mesoscale weather forecasts through the late 1990's which are superior to those currently provided by the older NGM. To accurately evaluate the Eta Model, several model forecast output fields were compared to the NGM for a common population of extratropical cyclones over a period of five months. The separate model forecasts were also evaluated against their own analysis. Selected fields included central sea level pressure. 12h central pressure change 1000-500 mb thickness at the cyclone center, and both convective and total precipitation at the cyclone center. Results indicated a consistent negative bias in forecast central pressure values for the NGM. and a positive bias for the Eta Model. Mean forecast position errors were nearly identical for both models through 36h with the Eta forecast position errors only slightly larger at 48h. Both models exhibited a slight cold bias in 1000-500 mb thickness fields at the cyclone centers with the NGM being greater. The Eta Model tended to forecast more precipitation in general and in particular the precipitation was higher for stable precipitation.

The effect of resolution on the depiction of central sea-level pressure for an intense oceanic extratropical cyclone is examined through a one-dimensional Fourier analysis. Profiles of sea-level pressure were manually interpolated along the latitude passing through the storm center from two subjective analyses and the 00, 24, and 48 h Nested Grid Model (NGM) forecasts, all valid at 0000 UTC 5 January 1989. At this time, the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) Intensive Observing Period 4 (IOP-4) cyclone attained its maximum intensity, with a central pressure of 936 mb at 41 deg N 58 deg W in an analysis prepared by Prof. Frederick Sanders.

During the period of 12 through 14 March 1993 a major snow storm, later described as a White Hurricane, formed over the Gulf of Mexico, moved east-northeast across the Florida panhandle, and then headed northeast along the eastern seaboard. The extreme weather produced by this storm was responsible for 243 deaths and $1 billion in property damage. Because the storm was accompanied by unusually strong jet streaks, a diagnostic of the storm kinetic energy contents and generation of kinetic energy was undertaken. The vertically integrated kinetic energy (IKE) and vertically integrated generation of kinetic energy (IGK) are shown to be effective tools in determining how jet streaks influenced the development of this storm. Specifically, IKE can indicate geographically where jet streak maxima are located, whereas IGK can provide a measure of the effect of transverse circulations aloft. In addition, IGK combined with IKE can indicate if the jet streak is weakening or strengthening. The data used in this case study were primarily the National Weather Service's Global Spectral Model aviation forecast and analysis. These data were further interpolated for use in VISUAL, which is a meteorological diagnostic and display program developed primarily at the Naval Postgraduate School.

Numerous studies have left little doubt that latent heat release (LHR) can significantly influence many features of extratropical cyclone systems. Recent experiments with the NCAR/PSU mesoscale model indicated that not only did different moisture parameterizations significantly affect model forecasts, but that forecasts for different cyclonic systems responded very differently to the parameterizations. Model output from the NCAR/PSU model is examined for two cyclonic systems, with four different parameterization experiments used to produce four forecasts for each system. The output was then examined in three and four dimensions to qualitatively and quantitatively determine the direct and indirect effects of latent heat release on model output. The results clearly showed the difference in the general dynamics of the two cyclones. One demonstrated a very strong reliance on diabatic processes for its early development, becoming more adiabatic late in its history, while the other initially developed very adiabatically and became more diabatic after about the mid-point of the forecast period. The cyclonic system that started out diabatically was more sensitive to moisture parameterization. The models clearly showed the differences between precipitation fields generated by the different parameterizations. In particular, allowing evaporation of precipitation in non- saturated layers greatly decreased the areal extent of light precipitation, while having minimal effect in areas of heavy precipitation.

Variations in marine stratocumulus microphysics during FIRE IFO 1992 are observed and analyzed through the use of NOAA 10/11/12 AVHRR satellite data. Maritime and continental aerosols in clear-air and cloudy regions are characterized by particle size index, optical depth, and low cloud analysis at visible and 3.7 pm wavelengths. Use of satellitedetected radiances to resolve aerosol type and distribution prove useful in determining implications of cloud reflectance changes due to modification by aerosol particles. Air masses were clearly defined and showed distinctive signatures in aerosol characteristics and cloud reflectances at 3.7 pm wavelengths. Air mass characteristic sources consisted of industrial aerosols out of Europe and desert dust from the Sahara Desert.

The effect of model resolution on the ageostrohic circulations and dynamics of a rapidly deepening extratropical cyclone that occurred during the Intensive Observing Period (IOP) 4 (4-5 January 1989) of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) is examined using the psi-vector technique proposed by Keyser, et al. (1989). A comparison of forecasts made by the National Meteorological Center's Nested Grid Model (NGM) using operations (C-grid_ and double-resolution (D-grid) versions indicated pressure and frontal evolution differences between the two forecasts. The IOP-4 cyclone was observed to deepen by 60 mb in 24 h to a central pressure of 936 mb. The NGM C-grid forecast attained a central pressure at 0000 UTC 5 Jan of 959 mb, while the D-grid forecast attained a central pressure of 949 mb. Differences in this laterally coupled jet streaks between the C- and D-grid forecasts enabled the D-grid forecast to depict stronger transverse ageostrophic circulations that produced stronger ascent and greater spin-up of the low-level cyclone.

The influence of high resolutions sea surface temperatures (SST) on Nested Grid Model (NGM) predictions of rapid marine cyclogenesis is examined. Satellite data provides a gridded SST analysis with a resolution of 50 km. Forecasts using the operational "blended" SST analysis with a neutral stratification assumed in the calculation of surface exchange coefficient over the ocean are compared to forecasts using the high resolution SST analysis with a stability dependent surface exchange coefficient. Further comparison is made to NGM forecasts with no surface fluxes. This study covers the Intensive Observation Period (IOP) 5 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA). Results show little sensitivity of central pressure and storm position to the high resolution SSTs. However, differences in mesoscale features are present, primarily surface fluxes, precipitation, and frontal circulations.

NOAA-7 AVHRR data from April 1982 was used to perform global-scale analysis of aerosol particle characteristics. Mahony's (1991) water vapor correction was incorporated into the AVHRR multichannel satellite data processing technique used by Frost (1988). Channel 4/Channel 5 brightness temperature difference was used as an estimate of water vapor content in an air column. Greatest measured water vapor content was at the equator, decreasing toward the poles. Applying the correction reduced the aerosol particle size index, resulting in an increase in aerosol optical depths. In addition, the high particle size index over the low latitudes in the southern hemisphere noted by Frost, was reduced significantly after applying the correction. A comparison was made between Frost's values for the variable two-term Henyey-Greenstein phase function and those derived with the water vapor correction. The basic shape of the curve is similar to that determined bv Frost.

This study was done to describe the synoptic and mesoscale events associated with the development of fog and stratus along the Central California Coast during the 30 April to 5 May 1990 period. These events were compared and contrasted to the synoptic and mesoscale evolution found for stratus surge and Catalina Eddy events. Based on the analysis, the formation of the stratus and fog was found to be initiated by the movement of an upper- level cut-off low and a shortwave ridge. Their movements provided increased subsidence and upper-level negative vorticity advection (NVA lover Southern California, which, in turn, produced higher pressure over the Vandenburg region. This coupled with relatively lower pressure over Oakland, set up flow conditions that lead to the formation of the stratus and fog. The Vandenburg/Oakland pressure gradient produced southerly flow, which carried warm moist air over relatively cooler water. The moist air condensed and stratus and fog developed.

The mesoscale vertical structure of an explosively deepening oceanic cyclone on 19-20 January 1989 during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) was studied. Hand analyses of height, temperature, and dewpoint, and cross-sections of 6 and 6, were prepared using aircraft and sounding data through the warm-frontal region in order to document the vertical structure. The results showed that the initial disturbance formed under a region of strong upper-level confluence between a southern jet streak and an approaching upper-level short-wave from the northwest. Upper-level frontogenesis associated with the confluent flow was strong enough to produce tropopause folding and stratospheric extrusion as low as 700 mb about 750 km upstream from the surface low prior to rapid deepening. The mesoscale analyses during the initial occlusion phase showed the upper-level temperature and moisture patterns spiraling around the low center with strong warm air advection occuring under a pocket of cold air aloft, producing significant convective instabilty. The cross-sections of 6f throughout the rapid deepening period showed unstable conditions, which suggests that moist potential instability in the warm frontal region was a factor in the rapid development of this storm.

The mesoscale surface structure of an explosively deepening storm that developed during Intensive Observation Period (IOP) 5 (18-20 January 1989) of the Experiment on Rapidly Deepening Cyclones over the Atlantic (ERICA) was examined to determine the influence of surface forcing on explosive cyclogenesis. Aircraft, buoy and ship observations were converted to a 20 km gridded data set in order to generate objective analyses of the surface pressure and temperature fields comparable to the best hand analyses. The Brown-Liu boundary layer model was then used to calculate surface sensible heat fluxes from the gridded data sets. These analyses showed that the most significant feature that distinguished the IOP-5 storm from a typical nonexplosive storm was the region of sustained positive heat fluxes that occurred east of the low center. This feature, combined with substantial warm advection and conditions of moist symmetric neutrality in the baroclinic zone of the warm front, supports destabilization of the boundary layer and enhanced low-level baroclinicity. Thus, the positive heat fluxes fuel the convective transport of heat and moisture to the upper atmosphere and enhance the sensible and condensation heating that contribute to explosive cyclogenesis

A method for resolving the mesoscale distribution of precipitation over mountainous regions is developed using synoptic-scale analyses and topography with a 40 km resolution. The method consists of calculating the saturated moisture flux at a level assumed to be the cloud base and correlating this quantity with observed precipitation. General correlation coefficients ranged from-0.2 under conditions poorly represented by the synoptic surface analysis to -0.55 when theses analyses are more representative of actual forcing. When applied regionally, correlation improved dramatically, suggesting potential incorporation into precipitation forecasts over mountainous areas. Over wider regions of less defined topography, correlation is weaker but is still an improvement over the current synoptic-scale precipitation forecast products.

The effect of latent heat release on the development of a rapid deepening extratropical cyclone that occurred during Intensive Observation Period (IOP) 5 (18-20 January 1989) of the Experiment on Rapidly Deepening Cyclones over the Atlantic (ERICA) is examined usinf a diagnostic height tendency equation. Data consist of Nested Grid Model (NGM) forecasts executed with and without latent heating feedback. Withholding latent heat significantly decreased the intensity of not only the surface cyclone, but its associated 500 mb trough/ridge system as well. Propagation speed differed only slightly between the two forecasts, allowing the differences in intensification to be explored through height tendency differences between the two forecasts. Model results show that at 500 mb, latent heat release affects the height tendencies primarily, through indirect means, chiefly by enhancing vorticity advection. Differential thermal advection and vertical advection of static stability tended to offset each other, as did vertical advection of vorticity and tilting effects. A height anomaly due to latent heat release was located downstream of the 500 mb trough and served as a focus for forcing differences associated with latent heating.

During the period of 12 through 14 March 1993 a major snow storm, later described as a White Hurricane, formed over the Gulf of Mexico, moved east-northeast across the Florida panhandle, and then headed northeast along the eastern seaboard. The extreme weather produced by this storm was responsible for 243 deaths and $1 billion in property damage. Because the storm was accompanied by unusually strong jet streaks, a diagnostic of the storm kinetic energy contents and generation of kinetic energy was undertaken. The vertically integrated kinetic energy (IKE) and vertically integrated generation of kinetic energy (IGK) are shown to be effective tools in determining how jet streaks influenced the development of this storm. Specifically, IKE can indicate geographically where jet streak maxima are located, whereas IGK can provide a measure of the effect of transverse circulations aloft. In addition, IGK combined with IKE can indicate if the jet streak is weakening or strengthening. The data used in this case study were primarily the National Weather Service's Global Spectral Model aviation forecast and analysis. These data were further interpolated for use in VISUAL, which is a meteorological diagnostic and display program developed primarily at the Naval Postgraduate School., http://archive.org/details/theevolutionofje1094539707, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.